In obtaining the electrical characteristics of components and packaging structures, such as integrated circuits and multilayer ceramic substrates, it is imperative that the connecting paths from the tester to the device or structure under test, have a controlled electrical environment so as not to distort the test signals and test results. This is especially important in light of the ever increasing circuit speeds and density of the components under test.
Also increasing, in addition to the circuit speeds of the integrated circuits are the number and density of the interconnection pads on the integrated circuit device and the packaging substrate. Namely, the density of the circuitry on a monolithic device is increasing as the art advances. This increase in circuit density in an integrated circuit, in many, if not all instances, dictates a greater number and density of the connection pads on an integrated circuit. Correspondingly, the number and density of connection pads on the packaging substrate must be increased to accommodate the increase in number and density of connection pads of the high circuit density integrated circuit. Further, as the circuit density and speed of the integrated circuit increases the conductive paths within the packaging substrate increase in number and density and their length must be reduced or at least not increased. These factors oppose from a practical, or fabrication point of view, the ability of a contacting system to achieve a minimum acceptable distortion environment. These factors, as the art progresses, render the testing of integrated circuit devices, and interconnecting packaging structures more difficult. As the art progresses, the testing problems requiring solution are many and complex. Included in these test problems are the electrical environment, namely the electrical contacting of a densely spaced array of pads with each electrical connection having substantially equal and minimum uniform impedance characteristics. In testing the electrical connections to the pads must be made rapidly, and precisely, and must not place undue stress on, or mechanically damage the pads.
A major portion of the electrical path from the tester to the device under test and return is used for the space transformation function. It purpose is to take a large multiplicity of electrical conductors from the tester, which are relatively spaciously arrayed, and transform them into a highly dense array, similar to, or identical to, the device input output pad density pattern. Since the conducting path length from the tester to the device under test is dominated by the space transformer, for electrical testing to be done successfully, a constant impedance environment is necessitated.
Reference is made to United States Patent Application, now U.S. Pat. No. 3,911,361, Ser. No. 484,052, by Ronald Bove' et al., filed on June 28, 1974, entitled "Coaxial Array Space Transformer" and of common assignee herewith.
U.S. Pat. No. 3,911,361, is directed to circuit means for connecting a high speed electronic tester to a high circuit density monolithic device under test and where said circuit means includes a unitary structural combination of a space transformer and a probe structure, said space transformer and said probe structure being mechanically and electrically mated to provide a plurality of discrete physical electrical contacts with said device under test, said space transformer including: a printed circuit board having a plurality of discrete electrically conductive contact areas and at least one relatively large contact area; a densely spaced array of discrete electrical contacts; said densely spaced array of discrete electrical contacts being supported by and maintained in spaced relationship one to another by a material having predetermined dielectric characteristics; a plurality of coaxial cables; each, of said coaxial cables having an inner conductor, an outer ground shield and dielectric material maintaining said inner conductor and said outer ground shield in spaced relationship; each of said inner conductors of said plurality of coaxial cables being connected between a predetermined one of said plurality of discrete electrically conductive contact areas on said printed circuit board and a predetermined one of said densely spaced array of electrical contacts; a plurality of metallic plates for supporting said plurality of coaxial cables in spaced relationship; connection means for electrically connecting in common each of said plurality of metallic plates, each of said outer ground shields of said plurality of coaxial cables, and said relatively large contact area on said printed circuit board; said probe structure having a plurality of electrically discrete buckling beam probes; each of said buckling beam probes makingg physical and electrical contact with a predetermined one of said densely spaced array of discrete electrical contacts; each of said buckling beam probes having a length many times its cross-sectional area whereby the probes buckle when an axial load is applied thereto.
Reference is made to U.S. Pat. No. 3,731,191 granted May 1, 1973 for a "Micro-Miniature Probe Assembly" to Robert L. Bullard et al. and of common assignee herewith.
U.S. Pat. No. 3,731,191 is directed to a multi-probe test circuit assembly particularly adapted for producing low resistance electrical connections to a semiconductor component of which the electrical parameters are to be evaluated.
In accordance with the invention disclosed and claimed in U.S. Pat. No. 3,731,191, a contact apparatus is provided in which a plurality of probe elements are fixedly held by a common support housing in a fixed array corresponding with the terminal contact pattern of the circuit device to be engaged for testing. Essentially, the probe elements comprise individual tubular probe guides with individual probe wires, or the like, removably contained and compressible within the probe guides. Fixation of the probe elements in the desired array is provided by an encapsulation housing including a support plate portion of the support housing having a plurality of openings arranged to correspond with the test contact pattern of the circuit device. One end of each of the tubular probe guides is attached to the support plate within the plate openings while the other end is held within the housing preferable adjacent and in abutment with a pressure plate opposite the remote ends of the probe guides. The probe wires are designed such that when fully inserted within the probe guide, they extend a controlled amount beyond the end of the housing support plate while the remote ends of the probe wires abut the pressure plate. The tubular probe guides are high conductivity material while the probe wires are conductive material having high resistance to abrasive wearing. Electrical circuit continuity is made by surface contact of the probe wires within the probe guides which are in turn connected to external connecter boards or the like mounted on the housing and having provision for connection to external test circuits or the like.
In U.S. Pat. No. 3,731,191, the probe guides are preferably curved between their ends within the housing. Thus, when contact is made with a test terminal, the probe wires have a spring-like quality and are compressible within the probe guides, the curvature and spring-like qualities of the probe wires causing electrical contact to occur very close to the contact end of the probe guide. Thus, only a short length of the relatively high resistance probe wire is in the electrical circuit while the high conductivity probe guide acts as the principal electrical connection with the external circuits. Since the probe guides and probe wires are conductive, the contact apparatus is essentially made of dielectric materials, particularly the support plate and the pressure plates. In addition, the probe guides are completely encapsulated within a dielectric material so that the probe elements are mutually electrically insulated as well as being held rigidly in position.
Reference is made to U.S. Pat. No. 3,806,801 granted Apr. 23, 1974 to Ronald Bove, directed to a "Probe Contactor Having Buckling Beam Probes", and of common assignee herewith.
U.S. Pat. No. 3,806,801, discloses a probe contactor in which each of the probes will exert a substantially constant force on each of the pads on the chip irrespective of the relative heights of the pads on the chip as long as the pads on the chip have their height within the predetermined range in which the probes can engage the pads. This is accomplished by forming each of the probes with a length many times its cross sectional area so that each of the probes may be deemed to be a beam. Each of the probes is designed so that it will deflect over a range when a predetermined force is applied at its end engaging the pad to axially load the probe so as to prevent any additional force, beyond the predetermined force, being applied to the pad due to engagement of the pad with the probe.
Reference is made to U.S. Pat. No. 3,806,800, granted Apr. 23, 1974, to Ronald Bove and Eric M. Hubacher, directed to "Method and Apparatus for Determining the Location of Electrically Conductive Members on a Structure", and of common assignee herewith. In U.S. Pat. No. 3,806,800, the electrically conductive pads on a semiconductor chip or the engineering change pads on a multilayer substrate are located electronically relative to probes which are in a predetermined orthogonal orientation, so that the particular probe or probes in engagement with each of the pads is determined. Then, the electrical characteristics of any electrical unit connected to each of the pads is ascertained through selectively controlling the electrical power supplied through the probes to the pads in a controlled manner.
U.S. Pat. No. 3,835,381, granted Sept. 10, 1974 to O. R. Garretson et al., entitled "Probe Card Including A Multiplicity of Probe Contacts and Methods of Making" discloses a probe card useful in testing the effectiveness and utility of semiconductor devices and hybrid circuit substrates prior to the application to such devices and substrates of terminal leads for interconnection with other components. The probe card includes a unitary electrically conductive probe assembly including a multiplicity of closely spaced conductive probes arranged in a radiating array to provide a multiplicity of contact tips adapted to be pressed with uniform pressure and contact resistance on the terminal pads of semiconductor devices and hybrid circuit substrates.